The invention relates to an exhaust gas turbocharger with a compressor for an internal combustion engine, the compressor having a compressor inlet and a bypass channel for recirculating partially compressed air to the compressor inlet.
An exhaust gas turbocharger of an internal combustion engine has an exhaust gas turbine which is arranged in the engine exhaust gas duct and is driven by the exhaust gases of the internal combustion engine, and a compressor in the intake duct of the engine with a compressor impeller which is driven by the turbine via a shaft. Combustion air is fed at atmospheric pressure to the compressor impeller via an inflow channel, which combustion air is compressed to an increased charge pressure by the compressor and then supplied to the cylinders of the internal combustion engine.
The development of supercharged internal combustion engines of this type with a desired torque behavior increasingly requires widened compressor characteristic diagram or performance graph ranges both for commercial vehicles and for passenger vehicles. The compressor characteristic diagram, in which the total pressure ratio (ratio of the output pressure to the input pressure of the compressor) is plotted with respect to the mass throughput, is limited firstly by the pumping limit of the compressor, that is to say the minimum possible volumetric delivery, and secondly by the choke limit of the compressor, that is to say the maximum possible volumetric delivery. Stable operation of the internal combustion engine at constant rotational speeds is possible between the pumping limit and the choke limit. In the case of lower mass throughputs, that is to say before reaching the pumping limit, stable operation of the internal combustion engine cannot be carried out because of pump surges. The exhaust gas turbocharger is often damaged in this connection, often after only a short operating time.
Measures to stabilize the characteristic diagram have therefore been developed for some time, which measures also make it possible to shift the pumping limit position to lower mass throughputs, as a result of which the drive torque and the acceleration torque or the maximum possible engine torque of the internal combustion engine can be increased significantly.
It is proposed as a measure to stabilize the performance graph to provide a bypass channel in the form of an annular gap within the compressor housing around the wheel contour of the compressor impeller parallel to the inflow channel. The bypass channel usually comprises a first flow opening upstream of the inlet edge of the compressor impeller, a second flow opening downstream of the inlet edge of the compressor impeller and an annular chamber which connects these two flow openings. The bypass channel which extends parallel to the inflow channel results in bypass mass flows which, in comparison with structurally identical apparatuses without a bypass, make a shift possible toward smaller or larger mass flows in the region of the pumping limit and in the region of the choke limit.
An exhaust gas turbocharger having a compressor of this type with a bypass channel is described, for example, in DE 196 47 605 C2. In this case, the opening regions of the first and the second flow openings of the bypass channel are additionally of variable design, so that the compressor characteristic diagram can be further optimized near the pumping limit and/or the choke limit.
A further exhaust gas turbocharger of this type is known from DE 198 23 274 C1. In this compressor, an additional wall element is provided for adjusting the opening region of the first flow opening of the bypass channel upstream of the compressor impeller inlet. Moreover, struts are provided for holding a wall section of the bypass channel so as to form an axial guide vane structure, in order to impart a swirl to the air mass flow through the bypass channel. The document does not contain more detailed information about the construction of said struts.
Furthermore, it is known in this context to arrange a guide vane structure or a plurality of guide vane structures in the inflow channel upstream of the compressor impeller, in order to impart a swirl to the air mass flow, which swirl has a favorable effect on the functional behavior of the compressor impeller, in particular in the limit areas of the compressor characteristic diagram. Arrangements of this type are disclosed, for example, by documents DE 102 33 042 A1, DE 103 29 281 A1 and EP 0 749 520 B1.
It is an object of the present invention to provide a compressor for an internal combustion engine, with an improved bypass channel which provides for a more stable shift of the pumping limit of the compressor and to facilitate an adaptation of the measure which stabilizes the characteristic diagram to a particular internal combustion engine.